The trend in very-large-scale integration (VLSI) technology has resulted in narrower interconnection lines and smaller contacts. Furthermore, integrated circuit designs are becoming more complex and denser. More devices are compressed in integrated circuits to improve performance. With higher current density, integrated circuits become more susceptible to electromigration (EM) causing the circuits to fail.
EM is a phenomenon that, at higher current density and/or increased device temperature, causes electron momentum to be transferred to atoms in thin film metallic conductors (e.g., signal nets) causing a net atomic flux. The atomic flux leads to voids which can cause a circuit to break open or to have hillocks, e.g., accumulation of metal leading to shorts with adjacent metal lines (e.g., signal nets).
Moreover, when there is too much current density through an interconnect for an extended period of time, resistance of the interconnect increases. The increased resistance results in self-heating and metal disintegration. The operating frequency and the reliability of semiconductor circuit are also deteriorated.